Visibility analysis of oceanic blue space using digital elevation models

Published evidence shows that views to blue spaces (e.g. ocean, lake, and river) have positive effects on humans' health and mental well-beings. However, quantitative assessment of blue space visibility is challenging for large spatial areas with complex terrain or built environment. The assessment approach introduced in this study applied an innovative sampling strategy which generalizes blue space as a lattice of points and calculate visibility of all the points within a continuous area. Compared to traditional viewpoint-based visibility analyses, this approach can assess blue space visibility over a large area at a fine spatial resolution. The raster output can be overlaid with data recorded at different spatial units to study the associations between blue space visibility and socio-economic and health disparities. Additionally, this approach can be applied to assess impact of buildings to blue space visibility over space by comparing outputs generated from different digital elevation models (DEM). The utility of this approach was demonstrated in a case study in the island of O'ahu, Hawaii, which finds that: (1) wealthier and older people possess higher share of ocean visibility; (2) man-made buildings have caused large shrink and redistribution of ocean visibility; (3) high-rise buildings have particularly high and extensive impact to ocean visibility. The findings suggest that improved environmental assessment processes and planning policies are needed to mitigate the inequality of visible blue space in different population groups and preserve the shrinking visible blue space in the process of urban development.